Alloy Coating Apparatus and Metalliding Method

ABSTRACT

A material ( 20 ) is coated to enhance and add desirable properties through a metalliding process employing an atmosphere ( 14 ) substantially free of oxygen and an electrolytic bath ( 18 ) within the atmosphere ( 14 ). An electrically conductive substrate ( 20 ) to be coated is submerged within the bath ( 18 ) as a cathode ( 20 ) along with multiple anodes ( 26 ), each anode ( 26   a,    26   b,    26   c ) having a distinctive composition from the other. A variable power source ( 30 ) provides distinctly selected current densities to each of the anodes ( 26 ) so as to result in a coating of the substrate ( 20 ) by each anode material ( 26   a,    26   b,    26   c ) in proportion to the applied current densities.

FIELD OF INVENTION

The present invention generally relates to coating a base metalcomposition and in particular to metalliding including diffusing a basemetal composition with two or more pre-selected metals in a fused saltbath.

BACKGROUND

As is well known in the art and as discussed in the Scientific American,August 1969 publication article “Metalliding” by Newell C. Cookregarding his work at the General Electric Research and DevelopmentCenter, the disclosure of which is herein incorporated by reference inits entirety, the association of one metal with another often results inproperties that are superior to those of either metal alone. In additionto the traditional alloying (mixing die metals in the molten state) andplating (attaching one metal to the surface of the another), metallidingdiffuses the atoms of one metal into the surface of another. Thediffused metal becomes an integral part of the surface of the othermetal, instead of being only mechanically attached to the surface as inplating. Metalliding is one form of alloying, except the alloy is onlyat the surface.

The diffusion is achieved by means of a high-temperature electrolyticprocess. The diffusing metal, serving as an anode, and the receptormetal, serving as a cathode, are suspended in a bath of molten fluoridesalt. When a direct current passes from the anode to the cathode, theanode material dissolves and is transported to the cathode. There theanode material diffuses into the cathode, giving rise to an alloyedsurface. As a result, a number of desirable changes in properties areachieved.

By way of example, the diffusion of boron into the surface of molybdenumproduces a surface with a hardness approaching that of diamond. Ifsilicon is diffused into molybdenum, the resulting material can be usedin air for hundreds of hours at white heat, whereas untreated molybdenumburns in air at dull red heat and is rapidly destroyed. When berylliumis diffused into copper, the copper is made stronger, more resilient,harder and more resistant to oxidation while retaining its excellentelectrical conductivity. Bonded steel may be made as hard as tungstencarbide, titanided copper resists boiling nitric acid and corrosion inair and tantalided nickel becomes almost as resistant to corrosiveoxidation as pure tantalum.

As addressed by the Cook article, many benefits could be achieved ifsteel and other metals could be immersed in molten boron, silicon,chromium, titanium, tantalum and so on, but all of these metals melt atsuch high temperatures that the steel itself would melt on immersion inthem. Metalliding provides a simple, practical and broadly applicablemeans of alloying metal surfaces.

Further, the molten-salt technique disclosed by Cook can be used withmost of the metals on the periodic table as either the diffusing metalor the substrate. The fluxing action of the molten fluorides dissolvesfrom the surface of the cathode metal the oxide film that forms in airon all metals except gold and possibly platinum. Air oxide film on thesurface of a metal is always a barrier to the diffusion of other metalsinto the substrate. The clean surfaces created by the fluoride solventsenable the atoms being electrolytically deposited to make direct contactwith the atoms of the cathode's surface and allow diffusion to proceedat the maximum rate.

Boron and silicon are similar in reactivity, and so they are similar inthe range of their applications as metalliding agents. The metals thatcan be bonded and silicidied include vanadium, chromium, manganese,iron, cobalt, nickel, copper, niobium, molybdenum, technetium,ruthenium, rhodium, palladium, sliver, tantalum, tungsten, rhenium,osmium, iridium, platinum, and gold. The list contains most of thefamiliar structural metals. Bedding and siliciding can be accomplishedha a large number of salt mixtures but is usually done in a ternarycompositional lithium fluoride, sodium fluoride and potassium fluoride.

Boride coatings are exceptionally hard. On steel, they usually fallbetween 1,500 and 2,500 on the Knoop scale, and often they exceed 3,000.On simple steels and many alloy steels the coating develops a root likeattachment as the boron diffuses in; the coating is tightly anchored andmaintains its integrity even when the material is considerably deformed,The boride coatings usually have poor resistance to corrosion (except onstainless steels), but this can be remedied by lightly chromiding andsiliciding the boride layer. Bonded steels show great promise forbearings and for dies. At their present stage of development, they aretoo brittle to be used as cutting tools.

The alloy surfaces are firmly bonded because the diffusing atomspenetrate the original structure and become part of it. The coatings arenever porous because the original surface of the completely densesubstrate is nonporous, and in accommodating the new atoms the structureof the substrate is only rear-ranged and expanded. The alloy coating canusually be formed with a high degree of electrolytic efficiency. Controlof the coating's thickness can be quite precise. Most of the coatingsare formed in thicknesses of from one mil (0.001 inch) to five mils intwo to three hours. Some coatings develop more rapidly, becoming severalmils thick in only a few minutes, and others form quite slowly, takingtwo or three days to attain a thickness of one or two mils. Almostwithout exception, increasing the temperature has speeded up the coatingprocess. The alloys that are formed at the higher temperatures oftenhave different properties, and sometimes less desirable ones, than thealloys formed at a lower temperature. As the temperature approaches themelting point of the substrate metal or of the alloy surface beingformed, the rate of diffusion usually increases rapidly.

The fluoride solvent systems have a number of other advantages. First,they hold metalliding ions in solution. The alkali and alkaline earthfluorides combine with the fluorides of all other metals to producesoluble and highly stable fluometallate anions (negative ions). Hencethe agents dissolve in the molten fluorides whether those agents are asolid with a high melting point or a gas, usually only a small amount(less than 1 percent) of the fluoride needs to be dissolved in thesolvent fluoride for the metalliding reaction to take place. The solventsystem can be varied according to the type of reaction desired. Forexample, it is usually advantageous to include potassium fluoride iiithe solvent system for the siliciding and bonding reactions,fluorosilicate and fluoroborate ions are held much more tightly bypotassium ions than by sodium and lithium ions.

Second, the alkali and alkaline earth fluorides do not form solventcations that interfere with the alloying reaction. In general, the GroupIA and Group IIA metals do not dissolve in or form compounds with thestructural metals, primarily because the IA and IIA metals have atoms ofcomparatively large diameter. Therefore, fluoride salts of these metalsare inert solvents for most metalliding reactions because metal atomsthat are generated electrolytically from the salts do not dissolve inthe surface of the cathode or react with it. Before they move manyatomic diameters from the surface of the cathode they collide withfluometallate anions and promptly take away fluorine atoms. Thisliberates atoms, which then diffuse into the surface of the cathode.

Third, the fluoride solvents are excellent electrical conductors. Theyare so completely ionized in the molten state that current-carryingcapacity has never been a limiting consideration in forming diffusioncoatings. Moreover, the solvent fluorides are essentially noncorrosive,particularly when they are largely free of oxygen. They have still otheradvantages: they have low vapor pressure at operating temperatures, theyresist displacement reactions by anode metals and they have a highsurface tension (so that little of the all, is removed when a coaledpiece is taken out of the metalliding bath).

The properties and functions of the fluoride solvents are the salienttechnical features of the metalliding process. While most metallidingreactions will sustain themselves through a battery-like action of theinternally generated electromotive force, an external electric currentis usually imposed on the internal electromotive force, with the samedirection of flow in order to achieve a more uniform and higher currentdensity than the battery action will provide. In this way metallidingcan proceed from three to 10 times faster than with the self-generatedbattery action without exceeding the rate at which the alloying agentcan diffuse into the cathode substrate.

When the metalliding cell is operating as a battery, the polarity of thecathode is actually positive compared with the anode, whereas in platingthe cathode is always more negative than the anode. When in metallidingan additional current is applied from an external source at asufficiently low current (amperage) and diffusion occurs rapidly, theentire reaction can be run without the cathode's becoming negative. Ifthe flow of current is interrupted during the applied current reaction,a rapid return of the cathode to positive polarity indicates thatdiffusion is keeping up with deposition. Failure of the cathode toreturn to a positive polarity indicates that the anode metal is startingto plate the cathode instead of diffusing into it.

SUMMARY

The present invention relates to improved methods for metalliding a basemetal composition. The invention is further directed to processes forcoating and/or diffusing a base metal composition with two or morepre-selected metals in a fused salt bath. A material may be coated toenhance and add desirable properties through a metalliding processemploying an atmosphere substantially free of oxygen and an electrolyticbath within the atmosphere. An electrically conductive substrate to becoated is submerged within the bath as a cathode along with multipleanodes, each anode having a distinctive composition from each other. Avariable power source provides distinctly selected current densities toeach of the anodes so as to result in a coating of the substrate by eachanode material in proportion to the applied current densities. It hasbeen discovered that an extremely hard, corrosion and erosion resistant,uniform, adherent alloy coating can be formed on or diffused into aspecific group of metals employing multiple low current densities, thatis, total current densities in the range of 0.05-10 amperes/dm².

The present invention is herein described in an apparatus that maycomprise an atmosphere substantially free of oxygen and an electrolyticbath within the atmosphere. An electrically conductive substrate havinga surface thereof is at least partially submerged within the bath as isa plurality of elements. Each element is electrically conductive, andeach has a distinctive composition from each other. An external powersource is operable with the substrate and each of the plurality ofelements. The power source provides a selected current density to eachof the elements and to the substrate so as to result in a coating of thesubstrate by material from each of the plurality of elements within thebath in proportion to the current densities applied thereto.

A method aspect of the invention for applying a coating to a substratemay comprise providing an atmosphere substantially free of oxygen and anelectrolytic bath within the atmosphere, submerging an electricallyconductive substrate within the bath, submerging a plurality ofelectrically conductive elements within the bath, each element having adistinctive composition from each other, and providing a current densityto each of the plurality of elements. The current densities aresufficiently imposed for coating the substrate with material from eachof the plurality of elements within the bath in proportion to thecurrent densities applied to each of the plurality of elements.

By way of example, niobium, tantalum, titanium, silicon and other metalboride intermetallic coatings and alloy coatings and diffusions may beformed on specified metal substrate compositions by forming an electriccell containing the metal composition as the cathode joined through acircuit having multiple external electrical connections to two or moreanodes. By way of example for embodiments herein described, one anodemay be boron and the other(s) may include the metal(s) required to formthe alloy. A pre-selected fused electrolyte is used and may bemaintained at a temperature of at least 600 C., by way of example, butbelow the melting point of the metal composition. This cell generateselectricity, but a separate variable electromagnetic field or force(EMF) is impressed on each anode circuit portion to establish alloypercentages of each anode metal deposited on the cathode metal.

Variations in the direct current waveform have proved advantageous incertain applications. The total cathode current densities preferably donot exceed 10 amperes/dm². The anode metals diffuse into and/or onto thebase metal to form an alloy coating or diffusion onto or into thesubstrate composed of the anode metals and/or the substrate metal. Thisprocess is useful in making coatings on the substrate metals.

BRIEF DESCRIPTION OF DRAWINGS

For a fuller understanding of the invention, reference is made to thefollowing detailed description, taken in connection with theaccompanying drawings illustrating various embodiments of the presentinvention, in which:

FIG. 1 is a diagrammatical schematic illustration of one embodiment ofthe invention including multiple elements forming anodes each operablewith a voltage controller for providing a pre-selected alloy coatingonto a substrate as the cathode;

FIG. 2 is a diagrammatical illustration of one embodiment including atwo-element anode, one element of boron, a second of Niobium, within abath for coating a stainless steel turbine blade;

FIG. 3 is a diagrammatical photo-micrographic image of a two-elementalloy according to the teachings of the present invention illustratingniobium and boron on steel;

FIG. 4 is a perspective view a single blade having an alloy coatingaccording to the teachings of the preset invention; and

FIG. 5 is a diagrammatical photo-micrographic image of a two-elementalloy according to the teachings of the present invention illustratingtantalum and boron on steel.

DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which alternate embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

With reference initially to FIG. 1, one embodiment of the invention isherein described as an apparatus 10 comprising a housing 12 having anatmosphere 14 therein substantially free of oxygen. It has been foundthat an inert atmosphere and a vacuum provide effective environment forsupporting the metalliding process. A container 16 positioned within thehousing 12 includes an electrolytic bath 18. An electrically conductivesubstrate 20 includes a surface 22 to be coated submerged within thebath 18. As herein illustrated, the substrate 20 is a cathode for anelectrical circuit 24 and a plurality of electrically conductiveelements 26 is an anode within the circuit. Each element 26 a, 26 b, 26c of the anode has a distinctive composition from each other, as will befurther detailed later in this section, and each has its surface 28submerged within the bath 18.

With continued reference to FIG. 1, a power source 30 is connected tothe substrate (cathode) 20 and to each of the plurality of elements(anode) 26. Yet further, the power source 30 is operable with rheostats32 for providing a preselected current separately to each of theplurality of elements 26. By way of example, three rheostats 32 a, 32 b,32 c are herein described for providing a preselected current to theirrespective anode elements 26 a, 26 b, 26 c for resulting in a currentdensity to each of the elements 26 and the substrate 20. As a result, ametalliding reaction results and the substrate 20 is coated withmaterial diffusing from each of the plurality of elements 26 within thebath 18 onto the substrate 20 in proportion to the current densityapplied to each of the plurality of elements 26. As will be understoodby those of ordinary skill in the art, individual power sources may beemployed for each of the separate anode elements 26. Yet further, thetime required to apply the current will depend upon the source profile.By way of example, a half wave DC supply will typically need twice thetime to apply the current density that a constant DC supply.

By way of example, the elements 26 forming the anode may include anatomic element, a metal, a non-metallic material, and/or an alloy.

In accordance with the teachings of the present invention, and withcontinued reference FIG. 1, one process includes pre-selected metals, aswill be further detailed later in this section, employed as the anodes26 and immersed in a fused salt bath comprising alkali metal fluoridemixtures or mixtures of the alkali metal fluorides with calciumfluoride, strontium fluoride, barium fluoride, potassium fluoride,sodium fluoride or lithium fluoride and containing from 0.1 to 15% molepercent of the appropriate anode fluoride. For one embodiment, theelectrolytic bath comprises a fluoride salt. The bath may be fluoridesof calcium, lithium, sodium, potassium, rubidium, and cesium, by way ofexample.

The cathode 20 employed is a base metal upon which a desired deposit isto be made. Under such conditions, the anode metals dissolve in thefused salt bath and anode metal ions are discharged at the surface ofthe base metal cathode where they form an alloy deposit and/or diffusiononto or into the base metal to form a metallic or inter-metallic coatingand/or diffusion. As supported by the efforts of Newell C. Cook, abovereferenced, the apparatus 10 of FIG. 1 employed in metalliding reactionsincludes a metalliding agent, serving as the anode 26, dissolves in themolten fluoride bath 18, becoming positive ions because of the tendencyof the fluoride in the solvent to capture electrons. At the cathode 20,which include a submerged metal that is to be coated, electrons fromcurrent flowing externally through the apparatus reduce the ions toatoms of the anode metal, which atoms then diffuse into the surface 22of the cathode 20, giving the cathode/substrate 20 new properties. Whileexamples using two anode elements are herein presented below, by way ofexample, it is understood by those skilled in the art that multipleanode elements may be employed as desired.

The rate of dissolution and deposition of the deposited material is notself-regulating in that the rate of deposition onto and into the basemetal cathode 20 from each of the anode material elements 26 isdependent on the individual current externally applied.

The alkali metal fluorides used in accordance with the process mayinclude the fluorides of lithium, sodium, potassium, rubidium andcesium. However, it is desirable when available to employ a eutecticmixture to operate this process at a relatively low temperature.Mixtures of the alkali metal fluorides with calcium fluoride, strontiumfluoride or barium fluoride can also be employed as a fused salt in theprocess of this invention.

Attention to the chemical composition of the bath 18 is desirable ifdesirable coatings and/or diffusions are to be obtained. By way ofexample, the starting salt should be as anhydrous and as free of allimpurities as is possible or should be easily dried or purified bysimply heating during the fusion step. The process is desirably carriedout in the substantial absence of oxygen since oxygen interferes withthe process. As above described, the process may be carried out in aninert gas atmosphere or in a vacuum. By the term “substantial absence ofoxygen” it is meant that neither atmospheric oxygen nor oxides of metalsare substantially present in the fused salt bath. By way of furtherexample, desirable results were obtained by using reagent grade saltsand by carrying out the process under vacuum or an inert gas atmosphere,for example, in an atmosphere of argon, helium, neon, krypton, nitrogenor xenon.

It has been found that even commercially available reagent grade saltscan be further purified to desirably operate the metalliding process.This purification can be readily done by utilizing scrap metal articlesas the cathodes and carrying out the initial cleaning runs with orwithout an additional applied voltage, thereby plating out and removingfrom the bath those impurities which interfere with the formation ofhigh quality coatings.

The base metals coated in accordance with the process of this inventionmay include all metals and alloys of those metals having a meltingtemperature of above 500° C. The form of the anode is not critical.

In order to produce a reasonably fast plating rate and to insure thecoating and/or diffusion of the metals onto and/or into the base metalto form an alloy, it is desirable to operate the process at atemperature of from about 500° C. to 1100° C. It is useful to operate attemperatures of from 600° to 1100° C. The temperature at which theprocess is conducted is generally dependent to some extent upon theparticular fused salt bath employed. Thus, for example, whentemperatures as low as 600° C. are desired, a eutectic of potassium andlithium fluoride can be employed. Inasmuch as the preferred operatingrange for many coatings is from 900° C. to 1100° C., it is preferable toemploy lithium fluoride as the fused salt. As illustrated with referenceagain to FIG. 1, a heater 34 is operable with the container 16 holdingthe bath 18.

The amount of current applied to each element 26 can be measured with anammeter, which enables one to readily calculate the amount of anode(s)material being deposited on the base metal cathode and being convertedto the alloy layer. Knowing the area and electrical characteristics ofthe article (substrate 20) being coated/plated, the thickness of thecoating formed can be determined, thereby permitting accurate control ofthe process to obtain any desired thickness of the layer.

A voltage and thus the current applied may be varied to provide variablecurrent densities during the reaction, and to increase and control thedeposition rate of the alloy constituent coating being deposited withoutexceeding the diffusion and alloying rate of the anode(s) material intoand onto the base metal cathode. By way of example, the voltage may notexceed 1.0 volt and may fall between 0.1 and 0.5 volts during onemetalliding process.

Since the diffusion and coating rate of various anode materials into andonto the cathode article varies from one material to another withtemperature, and with the thickness of the coating being formed, thereis typically a variation in the upper limits of the current densitiesthat may be employed. Therefore, the deposition rate of the alloyingagents is adjusted so as not to exceed the diffusion and coating rate ofthe alloying agents into and onto the substrate material if highefficiency and high quality coatings are to be obtained. The maximumcurrent density for a desirable alloy coating and/or diffusions is 10amperes/dm.², when operating within the above addressed temperatureranges of this disclosure.

By way of further example, relatively low current densities (0.01-0.1amperes/dm.²) are often employed when diffusion and coating rates arecorrespondingly low, and when very dilute surface solutions or very thincoatings are desired. The composition of the diffusion coating ischanged by varying the current density of the individual anodes forproducing a composition suitable for one application. Due to factorsincluding a wide range of atomic sizes of elements, most extremely hard,corrosion and erosion resistant alloys cannot be created by layering oneelement on top of another, but must be delivered to the cathodesubstrate atom by atom in a correct proportion to create a desired alloycoating. The teachings of the present invention provide such desiredalloy coatings.

Generally, current densities to form subjectively desirable qualityalloy coatings and/or diffusions fall between 0.5 and 10 amperes perdm.² for the temperature ranges herein disclosed. When it is desirableto apply additional voltage to the circuit in order to shorten the timeof operation, the total current density will not exceed 10 amperes/dm.²,by way of example.

The power supply 30 (e.g. a battery or other source of direct current),is connected within the circuit 24 so that the negative terminal isconnected to the base metal being coated, the cathode 20 and thepositive terminal is connected to the anode 26. In this way, thevoltages of both sources are algebraically additive. As will be readilyapparent to those skilled in the art, measuring instruments such asvoltmeters, ammeters, resistances, timers, and the like, may be includedin the circuit to aid in the control of the process.

Because the extremely hard, tough, pore free, adherent corrosion anderosion resistant properties of coatings and diffusions are uniform overthe entire treated area, the coated metal compositions prepared by themetalliding process herein described has a wide variety of uses. By wayof example, the apparatus 10 as above described may be used to produceatomically bonded surface coatings such as niobium, titanium, tantalumand zirconium borides for wear and corrosion resistance, nuclear fuelrod layered zirconium boron applications and many other uses that willbe readily apparent to those skilled in the art as well as othermodifications and variations of the present invention in light of theabove teachings.

By way of example and with reference to FIG. 2, one embodiment of theinvention includes a two-element anode element, one of niobium 26(Nb)and one of boron 26(B) providing a niobium boride coating to a surfaceof a gas turbine blade 38 as the substrate 20. Such turbine blades 38are typically located in a front compressor section of an engine. Aniobium boride coating 40, as applied using the teachings of the presentinvention, provides a thick atomically bonded coating of niobium andboron as a niobium boride alloy (NbB) on a 1015 stainless steelsubstrate/cathode 20 as illustrated with reference to FIG. 3. Thiscoating 20 will be useful in covering both martensitic stainless bladesas well as titanium blades illustrated with reference to FIG. 4.

By way of example, if a alloy coating of niobium and boron as niobiumboride (NbB) is desired, equal current densities are applied to eachanode 26(Nb), 26(B). For anodes having equal surface areas within thebath, equal currents would be applied. Alternatively, an alloy coatingof niobium boride (NbB₂), also referred to as niobium di-boride, may bedesired. For this case, the current density for the boron anode 26(B)will be generally twice that applied to the niobium anode 26(Nb).Results have shown the current density generally has a linearrelationship to the amount of anode material applied.

The economic benefits of this coating to the airline industry areconsiderable. An aircraft turbine engine will require a re-build every8,000 to 15,000 hours depending on the make, model and age. The increasein fuel consumption due to loss of compressor efficiency from new tore-build or re-build to re-build is 5% or 2½% over the period. This lossis caused by erosion of the airfoil properties of the compressor blades.This erosion is due to the ingestion of airborne particles, particularlyduring landing and takeoff. The wear resistance of NbB is roughly 10times that of unprotected blades and because of certain technicalissues, (the fact that the coating is atomically bonded) would begranted FAA certification in less than 2 months. This fuel savings wouldsave American Airlines alone, (700 aircraft) somewhere around 300million dollars per year.

This NbB coating on titanium has other potential applications. Titaniumis a suburb material but it has very poor erosion properties and somecorrosion and friction (bearing) problems. A ½ thousandth coating wouldsolve many of those problems as NbB is significantly harder thantungsten carbide and very, very corrosion resistant. As furtherillustrated with reference to FIG. 5, a tantalum boride coating 40 on asteel substrate 20 provides desirable results. For both diagrammaticalphoto-micrographic images of FIGS. 3 and 5 taken from actualphoto-micrographic images, a fixture 42 used in testing the coatedsubstrate is also shown, but is not intended to form a part of theclaims invention.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that modificationsand alternate embodiments are intended to be included within the scopeof the claims herein presented.

1. An apparatus comprising: an atmosphere substantially free of oxygen;an electrolytic bath within the atmosphere; an electrically conductivesubstrate having a surface thereof submerged within the bath; aplurality of elements, each element being electrically conductive, andeach having a distinctive composition from each other and each havingsurfaces thereof submerged within the bath; and a power source operablewith the substrate and each of the plurality of elements, the powersource providing a current density to each of the elements and thesubstrate so as to result in a coating of the substrate by material fromeach of the plurality of elements within the bath in proportion to thecurrent densities applied thereto.
 2. The apparatus according to claim1, wherein at least one of the plurality of elements comprises at leastone of an atomic element, a metal, a non-metallic material, and analloy.
 3. The apparatus according to claim 1, wherein the element isselected from the group of atomic elements consisting of silicon (Si),niobium (Nb), boron (B), and tantalum (Ta).
 4. The apparatus accordingto claim 1, wherein the plurality of elements comprises two elementsincluding a first element of boron and a second element of niobium, andwherein the current densities applied to the first and second elementsprovides an alloy coating of niobium boride to the substrate.
 5. Theapparatus according to claim 1, wherein the substrate comprises steel.6. The apparatus according to claim 1, wherein the electrolytic bathcomprises a fluoride salt.
 7. The apparatus according to claim 6,wherein the flouride salt is selected from the group consisting offluorides of lithium, sodium, potassium, rubidium, and cesium.
 8. Theapparatus according to claim 1, wherein the atmosphere comprises atleast one of an inert atmosphere and a vacuum.
 9. The apparatusaccording to claim 1, wherein the power source operable with thesubstrate and the plurality of elements form an electrical circuitwherein the plurality of elements comprise an anode and the substratecomprises a cathode.
 10. An apparatus for applying a coating to asubstrate, the apparatus comprising: a housing having an atmospheretherein substantially free of oxygen; an electrolytic bath carriedwithin the housing; an electrically conductive substrate having asurface thereof submerged within the bath; a plurality of electricallyconductive elements, each element having a distinctive composition fromeach other and each having surfaces thereof submerged within the bath;and a power source connected to the substrate and to each of theplurality of elements so as to form an electrical circuit having theplurality of elements forming an anode and the substrate forming acathode within the electrical circuit, wherein the power source isoperable for providing a preselected current separately to each of theplurality of elements thus resulting in a current density to each of theelements and the substrate, and wherein a metalliding reaction resultsin coating the substrate with material diffusing from the plurality ofelements within the bath onto the substrate in proportion to the currentdensity applied to each of the plurality of elements.
 11. The apparatusaccording to claim 10, wherein the power source comprises a plurality ofpower sources operable with the plurality of elements for imposing thepreselected currents onto each of the elements forming the anode. 12.The apparatus according to claim 10, further comprising a heateroperable with the electrolytic bath for providing a heating thereof. 13.The apparatus according to claim 10, wherein at least one of theplurality of elements forming the anode comprises at least one of anatomic element, a metal, a non-metallic material, and an alloy.
 14. Theapparatus according to claim 10, wherein the substrate comprises atleast one of a metallic turbine blade and a single blade, and whereinthe plurality of elements forming the anode comprises a first anodeincluding niobium and a second anode including boron.
 15. The apparatusaccording to claim 10, wherein the electrolytic bath comprises afluoride salt, and wherein the flouride salt is selected from the groupconsisting of fluorides of lithium, sodium, potassium, rubidium, andcesium.
 16. The apparatus according to claim 10, wherein the atmospherecomprises at least one of an inert atmosphere and a vacuum.
 17. A methodfor applying a coating to a substrate, the method comprising: providingan atmosphere substantially free of oxygen and an electrolytic bathwithin the atmosphere; submerging an electrically conductive substratewithin the bath; submerging a plurality of electrically conductiveelements within the bath, each element having a distinctive compositionfrom each other; applying a current density to each of the plurality ofelements; and imposing the current densities sufficiently for coatingthe substrate with material from each of the plurality of elementswithin the bath in proportion to the current densities applied to eachof the plurality of elements.
 18. The method according to claim 17,further comprising selecting each of the plurality of elements from atleast one of an atomic element, a metal, a non-metallic material, and analloy.
 19. The method according to claim 17, wherein applying thecurrent density comprises forming each of the plurality of elements asan anode and the substrate as a cathode within the electrolytic bath,and wherein the electrolytic bath comprises a molten fluoride salt. 20.The method according to claim 19 wherein the cathode comprises at leastone of a metal turbine styled blade and a single blade, and wherein theplurality of electrically conductive elements forming the anode comprisea first anode including niobium and a second anode including boron, themethod thus coating the metallic blades with an alloy of niobium andboron.
 21. The method according to claim 19, wherein the plurality ofelements comprises two elements including a first element of boron and asecond element of niobium, and wherein the current density applying stepcomprises applying a current density to each of the first and secondelements for providing an alloy coating of niobium boride to thesubstrate.
 22. The method according to claim 21, wherein the currentdensity applied to the first element of boron is substantially equal tocurrent density applied to the second element of niobium so as to forman alloy coating on the substrate of NbB.
 23. The method according toclaim 21, wherein the current density applied to the first element ofboron is twice the current density applied to the second element ofniobium so as to form an alloy coating on the substrate of NbB₂.
 24. Themethod according to claim 17, further comprising a step of heating theelectrolytic bath and controlling a temperature thereof during thecurrent density imposing step.